1. Field of the Invention
The invention relates to a small motorized drive means for a movable functional element in a motor vehicle, especially for a motor vehicle closing means, with a drive element which can be driven by an electric drive motor and a carrier which transfers the force of the drive element to the functional element, and which, generally, is coupled to the drive element but not to the functional element. In particular, to such a drive in which the running electric drive motor, in one shutoff position, can be shut off by blocking the continued movement of the drive element in its direction of motion with the functional element, especially by the carrier striking a carrier stop surface on the functional element.
2. Description of Related Art
Small motorized drive means of the type under consideration have been installed in motor vehicles at a host of locations and are generally called "actuating elements." For example, such drive means have been used for motor vehicle closures, such as a motor vehicle rear hatch lock, and to all types of motor vehicle closing mechanisms including motor vehicle door locks, etc., and to other types of driven mechanisms in motor vehicles.
A motorized drive means used in a motor vehicle rear hatch lock of the type to which the present invention is directed (published German Patent Application DE-A-196 14 122 which corresponds to U.S. Pat. No. 5,934,767) moves a movable functional element of a detent pawl which holds a lock latch in the front catch or main catch by means of a catch projection. The drive element is made as a rotating element, specifically as a worm wheel or worm wheel drive, and can be driven in only one direction of rotation. By turning the drive element in the functionally stipulated direction of rotation, the carrier strikes an actuating surface of the detent pawl and lifts the catch projection of the detent pawl off the main catch of the lock latch. In the direction in which the carrier runs, behind the actuating surface on the detent pawl, is a carrier stop surface which lies in the path of motion of the carrier and stops the latter when the detent pawl is raised off the main catch, but for a detent pawl located in the overstroke position, it is located outside of the path of motion of the carrier and allows it to pass the carrier. The drive is turned off when the carrier strikes the carrier stop surface (blocked mode).
In the prior art which has already been explained, the electric motor is turned off as soon as the carrier strikes the carrier stop surface (blocked mode). Therefore, the functional element forms a more or less fixed stop for the drive element. The tolerances and deformation possibilities of the entire arrangement determine how the electric drive motor is "blocked" by interposition of the drive, and how the overall arrangement behaves after the power supply of the electric drive motor is turned off. In the prior art, the time of flow through the electric drive motor is controlled such that a permanently set over-travel time of, for example, 300 to 500 ms is provided. This permanently set over-travel time must also take into account the most extreme operating conditions.
For controlled shutoff of the electric drive motor which can be reproduced under all conditions a "hard" blocked mode with low tolerances and low inherent elasticity of the overall arrangement would be desirable. Aspects of operating reliability, noise development and wear, on the other hand, call for tolerances and a minimum amount of inherent elasticity of the overall arrangement.
Overall, it is extremely difficult to correctly take into account the reset forces which occur at the given elasticity of the overall arrangement, but also rebound effects under all operating conditions. Nevertheless, it is desirable, even essential for many applications, that the drive element reaches and maintains the shutoff position as accurately as possible, especially to prevent any adverse effect on further operation of the drive means when the following control commands are shut off.
The aforementioned problem of the opposing objectives of obtaining a "hard" blocked mode with "soft" (specifically elastic) characteristics has already been recognized (published European Patent Application No. EP-A-0 684 356). The approach found there works with a spring acting in both directions between the drive elements and a carrier which is tensioned when the carrier strikes the carrier stop surface. The spring path made available, in this way, which the drive element can still traverse with the carrier fixed is used to shut off the electrical drive motor (as always), the spring force then causing reset of the drive element opposite the motion into the shutoff position defined by the carrier. It has already been recognized in this prior art that the inertia of masses of the system leads to the carrier rising somewhat from the stop surface in the backward motion and comes to rest only at a short distance from the stop surface. In practice, it has been shown that the shutoff position defined in this way cannot be reproduced exactly enough, with the consequence of malfunctions.